Internal combustion engine performance and emissions can be improved by employing variable event valvetrains. One type of variable event valvetrain uses electrically actuated valves to regulate gas flow into and out of cylinders of an engine. Operation of electrically actuated valves is not constrained by a physical connection to the crankshaft or camshaft. Therefore, the timing (opening and closing) of electrically operable mechanically actuated valves may be varied with engine operating conditions to improve engine performance, efficiency, and emissions. However, at cold operating temperatures, frictional losses in the electrically operable mechanically actuated valve increase non-linearly and additional electrical energy is necessary to operate a valve. Further, the increased mechanical viscous friction changes the valve response and can also increase the complexity of controlling valves under varying operating conditions.
One embodiment of the present description includes a method to improve the performance of an electrically actuated valve operable in an internal combustion engine, the method comprising: supplying a time-varying current to at least a coil of an electrically operable mechanical valve actuator that operates a valve of a cylinder of an internal combustion engine; said time varying current increasing eddy currents as temperature decreases; and said time varying current decreasing eddy currents as temperature increases.
Heating an electrically operable mechanically actuated valve can lower the electrical power necessary to overcome valve mechanical forces so that valve operation is improved, at least during some conditions. In one embodiment, a time-varying current may be passed through an actuator coil to create a time-varying magnetic field. This field can induce eddy currents and hysteresis losses in nearby metal components (e.g., in the valve actuator armature). The eddy currents are transformed into thermal energy as their flow is restricted by the metal armature. This thermal energy can raise the temperature of oil that lubricates the actuator armature outer surface, thereby reducing the oil viscosity. Consequently, the amount of energy necessary to operate the valve can be reduced as the oil viscosity is lowered by heating. In addition, valve heating can improve valve response and may make a valve respond more predictably.
The present description can provide several advantages. For example, the approach can be used to reduce the amount of power consumed by valves during valve state transitions. Also, the method can allow valves to be heated before an operator requests a vehicle start, which may reduce engine starting time. In addition, valves may be heated in a variety of ways so that a specific heating method may be selected based on the geometry of an electrically operable mechanically actuated intake or exhaust valve, for example. Further, in some embodiments, heating may be targeted to specific areas of an electrically operable mechanical valve actuator so that energy may be used more efficiently. Further still, such heating can be localized to those valves that are intended to be operated during a cold start.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.